How It Works: The Chemistry of Plant-Based Dyeing

Natural dyeing is a process where plant-derived pigments bond with fibres to create lasting colours. Unlike synthetic dyes, which contain artificial chemicals, natural dyes rely on bioactive compounds found in plants, fungi, and insects. The process typically involves:
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  • Extraction: Drawing colour from plant materials using water, heat, or fermentation.
  • Binding: Using mordants or tannins to help the dye adhere to fabric.
  • Fixation: Ensuring colour fastness through pH adjustments and post-dye treatments.​

Mordants: Essential Substances That Fix Dyes to Fabric

Mordants are substances that help dye molecules attach to fibres, increasing durability and intensity. Common mordants include:
  • Alum (Potassium Aluminum Sulfate): A widely used, non-toxic mordant that brightens colours.
  • Iron (Ferrous Sulfate): Darkens hues and creates earthy tones.
  • Copper (Copper Sulfate): Produces greens and enhances blues.
  • Tannin-rich substances (e.g., oak galls, pomegranate peels): Help bind dye to fabric naturally, especially for plant-based fibres like cotton.
    Ethical and sustainable mordanting options include bio-mordants (like soy milk) and food-based tannins.

Mordant Ratios for Natural Dyeing

Mordants help fix dyes to fabric, improving colour fastness and intensity. The amount of mordant used depends on the Weight of Fiber (WOF), meaning the dry weight of the fabric or yarn being dyed. Here are the standard ratios for common mordants:
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Alum (Potassium Aluminium Sulfate)
- Most Common Mordant For protein fibers (wool, silk):
  • 10-15% WOF (e.g., for 100g fabric → 10-15g alum)
  • Use cream of tartar (5% WOF) to soften wool & brighten colours.
- For cellulose fibers (cotton, linen):
  • 15-20% WOF (e.g., for 100g fabric → 15-20g alum)
  • Requires a tannin pre-treatment for better bonding.

Aluminium Acetate
- Best for Cellulose Fibers Used primarily for cotton & linen
  • 5-8% WOF (e.g., for 100g fabric → 5-8g alum acetate)
  • Works best in a warm water mordant bath (~40°C).

Iron (Ferrous Sulfate)
- Colour Modifier & Mordant Used in low percentages to shift colours toward greys, greens, and muted tones.
  • 1-2% WOF (e.g., for 100g fabric → 1-2g iron sulfate)
  • Higher concentrations can weaken fibers, especially wool.
  • Can be added after dyeing to modify colour.

Tannin
- Required for Mordanting Cellulose Fibers Improves dye uptake in cotton, linen, and other plant-based fibers.
  • 8-15% WOF (e.g., for 100g fabric → 8-15g tannin)
  • Comes from sources like oak galls, myrobalan, sumac, quebracho, or pomegranate.
  • Can be used alone for soft beige tones or as a pre-treatment before alum.

Copper Sulfate
- Colour Modifier Used in small amounts to shift colours toward teal/green hues.
  • 1-2% WOF (e.g., for 100g fabric → 1-2g copper sulfate).
  • Can make colours more muted or earthy.

Soy Milk
-(Non-Metallic Binder for Cellulose Fibers) Used as a protein binder to help cellulose fibers hold dye better.
  • 1:5 ratio (1 part soy milk to 5 parts water) for dipping fabric.
  • Requires multiple dips and curing for at least a week before dyeing.
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Tannins: Natural Compounds That Improve Dye Absorption

Tannins are polyphenolic compounds found in many plants that help dyes bind to fibres, particularly cellulose fibres like cotton, linen, and hemp. They also influence colour and texture. Key sources of tannins include:
  • Gall nuts & Oak bark: Used traditionally for black and brown tones.
  • Pomegranate peel & Myrobalan: Produce golden-yellow hues.
  • Tea & Coffee: Can shift colours to deeper browns.
    Tannins can be used as a pre-treatment or incorporated directly into the dye bath for stronger colour results.

Understanding pH: How Acidity and Alkalinity Influence Colour

The pH level of a dye bath significantly affects the final colour outcome. Some dyes shift hues depending on whether the environment is acidic or alkaline:
  • Acidic conditions (e.g., adding vinegar or lemon juice): Tend to brighten reds, oranges, and pinks (e.g., shifting hibiscus from purple to red).
  • Alkaline conditions (e.g., adding baking soda or wood ash): Often turn dyes bluer or greener (e.g., modifying avocado pits from pink to purple).
    Testing pH with natural indicators like red cabbage juice can help determine how to manipulate colours naturally.

Colour Modifiers: Using Natural Agents to Shift and Enhance Tones

Modifiers are substances added after dyeing to shift colours subtly or dramatically. Some common natural modifiers include:
  • Iron: Darkens and mutes colours (e.g., turning golden yellows to olive greens).
  • Copper: Enhances greens and blues.
  • Salt: Sometimes deepens certain hues, especially with berry-based dyes.
  • Sunlight exposure: Can naturally fade or intensify colours over time.
    Experimenting with modifiers allows for a greater variety of shades from a single plant dye.

Safety & Sustainability: Best Practices for Eco-Friendly Dyeing

While natural dyes are often safer than synthetic alternatives, proper precautions ensure a non-toxic and environmentally friendly practice:
  • Work in a well-ventilated space when heating plant materials.
  • Wear gloves and a mask if using fine powders (e.g., iron mordant).
  • Use dedicated pots and utensils for dyeing (not for food).
  • Dispose of dye baths responsibly by diluting and composting where safe.
  • Prioritise ethical sourcing of plant materials—using local, foraged, or waste materials (like onion skins or avocado pits) supports sustainability.

Standard Water-to-Fabric (WOF) Ratios


  • Immersion Dyeing (Traditional vat dyeing): 2:1 or 1.5:1 WOF (e.g., 1.5–2 litres per 100g fiber)
  • Low-Water Immersion (Eco-Friendly Approach): 1:1 WOF (e.g., 1 litre per 100g fiber)
  • Concentrated/Hot Dye Baths: Sometimes even lower if the fiber absorbs the dye efficiently.
  • Factors to Consider:
  • Dense fibers (like wool) may require a bit more water for even dye penetration.
  • Lighter fibers (like silk or cotton) often need less water to prevent excess dilution of the dye.
  • Certain plant-based dyes require extra liquid for better extraction but not necessarily that much for dyeing.
  • Example: If you have 100g of fabric, you would use:
    • 3L of water (30:1 ratio).
    • 5L of water (50:1 ratio for delicate dyes).